The code called something that does not exist.
WHAT IT MEANS
A function was called, and PHP could not find it.
THE COMMON CAUSES
A missing PHP extension. The function exists in an extension that is not enabled. A function removed in a newer PHP version An incomplete file upload, leaving a file missing A plugin expecting another plugin that is not active A theme function called before the file defining it loaded
IF IT NAMES A COMMON EXTENSION FUNCTION
Functions beginning curl_, mysqli_, imagick, mb_, json_, or similar belong to extensions.
Enable the extension under cPanel > Select PHP Version > Extensions.
IF IT APPEARED AFTER A PHP VERSION CHANGE
The function was removed in the newer version. Switch back to the previous version, then update the code or the plugin responsible.
IF IT APPEARED AFTER AN UPDATE
A plugin or theme is calling something that no longer exists. Check for an update to that component, or disable it.
IF IT APPEARED AFTER AN UPLOAD
A file did not transfer completely. Re-upload the application files.
THE ERROR NAMES THE FILE
Which tells you which component is responsible.
